Dresden 2006 – wissenschaftliches Programm
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MM: Metall- und Materialphysik
MM 27: Diffusion I
MM 27.1: Vortrag
Donnerstag, 30. März 2006, 10:15–10:30, IFW B
Transient heterogeneity in long-range order kinetics with limited vacancy mobility — •David Reith1, Wolfgang Püschl1, Ferdinand Haider2, and Wolfgang Pfeiler1 — 1Institut für Materialphysik, Universität Wien, Boltzmanng. 5, AT-1090 Vienna, Austria — 2Institut für Physik, Universität Augsburg, Universitätsstrasse 1, D-86159 Augsburg, Germany
Limited availability and mobility of vacancies may imprint a heterogeneous character on phase transformations which are otherwise expected to be homogeneous. This effect was investigated by a MC residence time algorithm for disorder-order and order-order transitions in long-range ordered intermetallics of L12 and B2 structure. The calculation cell was subdivided into coarse graining cells and heterogeneity assessed by the mean square deviation of the local long-range order parameter. A transient increase of this measure over the statistical fluctuation for the respective annealing temperature was observed for the B2 structure, but not in the L12 case. This can be understood in view of the majority sublattice as an easy diffusion highway. The effect in B2 is even more pronounced when starting from a disordered state. For a homogenous character of the kinetics to be restored, an earlier intuitive criterion relied on the overlap of regions bounded by the mean quadratic random walk distances of neighboring vacancies. Whereas this condition is in fact met at a very early stage in the kinetics, true homogeneity is reached only when a significant fraction of lattice sites has been visited by a vacancy.